Polymer electrolyte fuel cells (hereinafter referred to as PEFCs) are configured to generate electric power and heat simultaneously through an electrochemical reaction between a fuel gas containing hydrogen and an oxidizing gas containing oxygen, such as air. A cell of a PEFC includes a MEA (Membrane-Electrode-Assembly) composed of a polymer electrode membrane and a pair of gas diffusion electrodes (anode and cathode), gaskets and electrically-conductive plate-shaped separators. The PEFC is typically formed in such a manner that plural cells are stacked together, both ends of the cells stacked together are sandwiched between end plates, and the end plates and the cells are fastened together by fastener members.
Each separator is provided on a main surface thereof manifold holes (reactant gas supply manifold hole and reactant gas discharge manifold hole) forming manifolds used to supply and discharge a fuel gas or an oxidizing gas (theses are referred to as reactant gases), and is provided on a main surface thereof contacting the gas diffusion electrode with groove-shaped reactant gas channels through which the reactant gas flows such that the reactant gas channels are connected to the manifold holes.
While flowing through the reactant gas channels, the reactant gas is supplied to the MEA and consumed through an electrochemical reaction inside the MEA. For this reason, in downstream regions of the reactant gas channels, a hydrogen concentration or an oxygen concentration decreases because of the consumption of the gas. As a result, in downstream regions of the reactant gas channels where the gas concentration is low, a power generation amount decreases and a power generation distribution according to the gas concentration is formed within a cell surface.
To solve such a problem, a fuel cell directed to increasing a power generation efficiency by making a gas concentration uniform within a cell surface by devising a shape of the gas channels is known (see, e.g., Patent literature 1). FIG. 9 is a schematic view showing a configuration of a main surface of a separator of the fuel cell disclosed in Patent literature 1.
As shown in FIG. 9, in a separator 200 in the fuel cell disclosed in Patent literature 1, a plurality of (three in FIG. 9) fluid channels 201˜203 (reactant gas channels) are composed of upstream portions of a substantially L-shape having upstream ends connected to an inlet (reactant gas supply manifold hole) 211, downstream portions having downstream ends connected to an outlet (reactant gas discharge manifold hole) 212, and midstream portions connecting downstream ends of the upstream portions to upstream ends of the downstream portions, and entirely have a spiral shape. In this structure, the upstream portions or the downstream portions of the fluid channels are not focused on specific regions of the separator 200, thereby making the reactant gas concentration uniform within an electrode surface.